"Their results have cleared the way for new technology based upon quantum information," the Royal Swedish Academy of Sciences said of the laureates -- Aspect, who is French, Clauser, an American and Zeilinger, an Austrian.

The scientists all conducted experiments into quantum entanglement, where two particles are linked regardless of the space between them, a field that unsettled Albert Einstein himself, who once referred to it in a letter as "spooky action at a distance".

"I'm very happy ... I first started this work back in 1969 and I'm happy to still be alive to be able get the prize," Clauser, 79, told Reuters by phone from his home in Walnut Creek, California.

Clauser, who worked at institutions such as Lawrence Berkeley National Laboratory and the University of California, Berkeley, during his career, said he had witnessed his initial work snowball into much larger experiments.

China's Micius satellite, part of a quantum physics research project, was constructed in part on his findings, he said.

"The configuration of the satellite and the ground station is almost identical to my original experiment. Mine was about 30 feet long, theirs is thousands of kilometers for quantum communication."

Asked to explain his work in layman's terms, he joked he does not understand it himself but added that the interactions it describes permeate almost everything.

"Probably every particle in the universe is entangled with every other particle," Clauser said, chuckling.

NATURE OF REALITY

French President Emmanuel Macron tweeted his congratulations to the winners, adding "Einstein himself did not believe in quantum entanglement! Today, the promises of quantum computing are based on this phenomenon."

Aspect, professor at Universite Paris-Saclay and Ecole Polytechnique, Palaiseau, near Paris, said he was happy his work had contributed to settling the debate between Einstein, who was sceptical about quantum physics, and Niels Bohr, one of the field's fathers. Both won Nobel physics prizes.

"Quantum physics, which has been fantastic field that has been on the agenda for more than a century, still offers a lot of mysteries to discover," Aspect, 75, told reporters.

"This prize today anticipates what will be one day be quantum technologies."

Zeilinger, 77, professor emeritus at the University of Vienna, told a news conference by phone after hearing the news that he was "shocked, but very positive."

In an interview after being awarded an honorary doctorate earlier this year, Zeilinger said that protected quantum communication over potentially thousands of kilometres via cables or satellite would soon be on the cards.

"It is quite clear that in the near future we will have quantum communication all over the world," he said at the time.

Quantum physics is the study of matter and energy at a subatomic level involving the smallest building blocks of nature, a realm governed by laws jarring with those of the classical Newtonian physics used in areas such as the motions of celestial objects.

In background material explaining the prize, the academy said the laureates' work involved "the mind-boggling insight that quantum mechanics allows a single quantum system to be divided up into parts that are separated from each other but which still act as a single unit."

"This goes against all the usual ideas about cause and effect and the nature of reality."

PRIZE 'LONG OVERDUE'

The laureates explored in ground-breaking experiments how two or more photons, or particles of light, that are "entangled" because they come from the same laser beam, interact even when they are separated far apart from each other.

Sean Carroll, Professor of Natural Philosophy at Johns Hopkins University and author of books on topics such as quantum mechanics, told Reuters the prize for the trio was long overdue.

"Even though the ... experimental techniques that these folks pioneered might not be directly applicable, they're laying the ground work for using quantum entanglement as a technological resource," he said.

The more than century-old prize, worth 10 million Swedish crowns ($902,315), is awarded by the Royal Swedish Academy of Sciences. Physics is the second Nobel to be awarded this week after Swedish geneticist Svante Paabo won the prize for Physiology or Medicine on Monday.

The physics prize has often taken centre stage among the awards, featuring household names of science such as Einstein, Bohr and Max Planck, and rewarding breakthroughs that have reshaped how we see the world.

($1 = 11.0826 Swedish crowns)